Fitting

Fitting of an edge-on in particular is a very tricky exercise. This is the method I am currently using:

Summary
Pass 1: Get the global parameters right using parameterised curves
Pass 2: Split in two sides and deal with both sides seperately using tabulated parameters and fixed velocity dispersion
Pass 3: Mask everything but the outer envelope of the PV diagram, such that the fit can deal with tabulated values and velocity dispersion free.